Bell X-5

Bell X-5
Country	USA
Role	Research aircraft
First flight	20 June 1951
Built	2

The Bell X-5 was the first aircraft capable of changing the sweep of its wings in flight. It was inspired by the untested wartime P.1101 design of the German Messerschmitt company. In contrast with the German design, which could only have its wing sweepback angle adjusted on the ground, the Bell engineers devised a system of electric motors to adjust the sweep in flight.

Source: Bell X-5 on Wikipedia

Bell X-5 Walk Around
Photographers	Vladimir Yakubov
Localisation	The National Museum of the USAF
Photos	74

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Bell X-5 Walk Around
Photographers	John Heck
Localisation	The National Museum of the USAF
Photos	16

The Quest for Versatile Flight

The Bell X-5 was a landmark experimental aircraft designed to test the feasibility of changing a wing’s sweep angle during flight. This “swing-wing” capability was intended to provide the best of both worlds: high lift for takeoff and landing (straight wings) and reduced drag for high-speed flight (swept wings). While inspired by wartime German research, the X-5 was the first aircraft capable of adjusting its sweep in the air, paving the way for future icons like the F-14 Tomcat and the B-1 Lancer.

Attribute	Technical Specification (Bell X-5)
Role	Experimental Variable-Sweep Research Aircraft
Crew	1 (Pilot)
First Flight	June 20, 1951
Powerplant	1 × Allison J35-A-17 turbojet
Thrust	4,900 lbf (21.8 kN)
Maximum Speed	1,150 km/h (715 mph) / Mach 0.98
Sweep Range	20° to 60° (Variable in flight)
Service Ceiling	15,200 meters (49,900 ft)

The Engineering of the Swing-Wing

The Compensation Mechanism: Simply sweeping a wing back moves the Center of Pressure rearward, which would normally make a plane dive uncontrollably. To fix this, the X-5’s wings translated forward along rails as they swept back, maintaining the aircraft’s balance.
German Origins: The X-5 design was heavily influenced by the unfinished Messerschmitt P.1101, which had wings that could be adjusted on the ground but not in flight. Bell engineers developed the complex electric motor and screw-jack system to enable in-flight movement.
Nose-Inlet Design: Like many early jets, the X-5 used a straight-through air intake in the nose, with the pilot sitting directly above the engine ducting.
Variable Drag: Pilots could change the sweep from 20° for landing to 60° for high-speed tests in less than 30 seconds.

Operational History & Safety Challenges

The Spin Problem: The X-5 was notoriously unstable in a spin. Because of the way the mass was distributed, once the aircraft began to spin, it was nearly impossible to recover. This flaw led to the loss of the second prototype and the death of Major Ray Popson in 1953.
Critical Data: Despite the risks, the X-5 program provided NASA (then NACA) and the Air Force with years of data on the aerodynamic loads and control difficulties of variable-geometry wings.
Legacy: The success of the “swing-wing” concept proved by the X-5 led directly to the development of the General Dynamics F-111 Aardvark and the Grumman F-14 Tomcat.
Preservation: The surviving X-5 is now part of the National Museum of the United States Air Force in Dayton, Ohio.